The adaptation of handheld communication devices, such as cellular telephones, text messaging devices and devices that support multiple different communication modes, has had a transformative effect on personal communications over the last decade. Such handheld devices have untethered their users from the fixed Plain Old Telephone System (POTS) land lines and desktop computers networked through the POTS and have provided ubiquitous communications and instant reachability.
In the future, it is expected that handheld communication devices (in particular cellular telephones) will carry a variety of personal and/or financial information, and be able to interface with a variety of disparate systems. Such enhanced cellular telephones are expected to be used for, among other things, file storage and transfer, identification, access control, and making and receiving payments—in addition to communication.
Given the need to interface with a variety of systems, such as systems in cars, home entertainment systems, public and private infrastructure, personal computers, etc, and the limited size of handheld communication devices, it is desirable to provide a limited number of interfaces or one very versatile interface. One form of interface is wireless. An example of a wireless interface that might be used to provide local connectivity is known as Bluetooth. However, in certain circumstances, wireless security concerns, interference issues, and power dissipation issues weigh in favor of using a wired interface. Thus, it is desirable to provide a very versatile wired interface for handheld communication devices.
It is desirable to be able to use such versatile wired interface to couple analog signals, such as audio signals, and a variety of types of digital signals. It is furthermore desirable to be able to transition between different types of signaling without causing any glitches. In particular, it is desirable to be able to transition to and from audio signaling without causing audible noise.